As a material of construction, copper and copper alloys constitute one of the major groups of commercial metals. Copper alloys, varying in composition to meet the requirements of specific applications, are widely used due to their excellent electrical and thermal conductivity, good corrosion resistance, adequate strength and ease of fabrication.
Aluminum-bronze alloys have taken a predominant position in construction applications because aluminum has been shown to be a highly effective element in enhancing the alloy's casting property, tensile strength and overall resistace to intergranular oxidation. Alloys of aluminum and copper are categorized in two commercially important types, the single-phase alpha solid solution alloys and the alpha-beta alloys.
Solubility limitations dictate that under equlibrium conditions, 9.8 weight percent aluminum is soluble in copper before the beta phase forms. In commercial nonequilibrium conditions, however, copper alloys containing in excess of 7.5 weight percent aluminum exhibit a two phase structure. Alpha phase alloys have excellent working properties and can be readily fabricated into tube and sheet plate. The commercially important aluminum bronzes contain 4-10% aluminum often in combination with other metals.
The annealing characteristics of alpha alloys resemble those of the well-known alpha brasses whereby annealing can be performed over a wide range of temperatures, from 430.degree.-760.degree. C. depending on desired properties. Aluminum-bronze alloys exhibit improved oxidation resistance at elevated temperatures than other copper-base alloys. Resistance toward oxidation, increasing with aluminum content, appears to be largely attributable to formation of aluminum oxide on the exposed surfaces.
This aluminum oxide film is resistant to most acid catalyzed attack and is distributed on the alloy surface to provide excellent resistant to smog catalyzed oxidation cased by urban nitrogen dioxide and sulfur dioxide. Furthermore, the addition of aluminum to copper tends to form a self-healing alloy surface film thereby substantially increasing the alloy's resistance toward impingement damage.
The structure and consequent heat treatability of aluminum bronze alloys appear to vary greatly with composition. For example, single phase alpha aluminum bronzes that contain only copper and up to 10% aluminum can be strengthened only by cold working and can be softened by annealing at 425.degree. to 760.degree. C.
Although single-phase binary alloys such as aluminum bronze 5% (95 weight percent copper, 5 weight percent aluminum) cannot be age hardened, the addition of particular elements such as cobalt and nickel produces alloys that are age hardenable.
Commercial aluminum-bronze alloys are designated by the Unified Numbering System (UNS) by numbers C60600 to C64200. The various coppers within this group have varying aluminum contents and consequently possess slightly different properties. All of these alloys, however, are primarily designed for applications requiring good corrosion-resistance and some examples follow.
Aluminum bronze 5%, C60800, used for condenser tubing, has a nominal composition, of 95 weight percent copper and 5 weight percent aluminum. This alloy exhibits good cold workability, fair hot formability and provides good corrosion resistance.
Lusterloy, designated C61500, possesses composition limits (weight percent) of 89.0 to 90.5 copper, 7.7 to 8.3 aluminum, 1.8 to 2.2 nickel and 0.015 lead, maximum. This alloy has a gold color and is typically used in decorative trim, architectural panels and tarnish-resistant articles. C61500 is characterized as exhibiting excellent corrosion resistance and good formability.
C63600, typically used for bolts, screw machine products and products requiring cold working, has composition limits (weight percent) of 93.5 to 96.3 copper; 3.0 to 4.0 aluminum; 0.7 to 1.3 silicon; and a maximum of 0.50 zinc; 0.20 tin; 0.15 nickel; 0.15 iron and 0.50 lead. C63600 is not recommended in applications requiring soldering, brazing and oxyfuel gas welding.
C63800, commonly known as Coronze, exhibits crevise corrosion resistance far superior to most other copper alloys. Coronze, exhibiting more resistance to stress corrosion than the nickel silvers, has composition limits (weight percent) of 93.5 to 96.3 copper; 3.0 to 4.0 aluminum; 0.7 to 1.3 silicon; and a maximum of 0.50 zinc; 0.20 tin; 0.15 nickel; 0.15 iron; and 0.05 lead. This alloy is typically used in springs, contacts, glass sealing and porcelain enameling.
There are certain disadvantages in using these prior art alloys. Alloys containing low proportions of aluminum do not develop the required proof stress and tensile strength when produced by standard hot working processes. Furthermore, it is generally accepted by those skilled in the art that in order to achieve the best combination of properties in copper-nickel-aluminum alloys, the ratio of nickel to aluminum should be in the region of 5:1.
It is known that copper alloys with an aluminum content of less than one-sixth of the nickel content result in an alloy possessing considerably higher ductility although proof stress and tensile strength are usually reduced. U.S. Pat. No. 3,399,057 discloses a cupro-nickel alloy composition which contains (by percent weight): 15-32% nickel, 1.5-3% aluminum, 4-6% manganese, 0.5-2% iron, and balance copper. While this patent does yield copper alloy compositions exhibiting higher ductility, this improvement is obtained at a loss of proof stress and tensile strength.
An aluminum-bronze alloy for a welding rod is disclosed in U.S. Pat. No. 2,430,419. This alloy contains 3 to 15 weight percent aluminum; 0.1 to 5 weight percent iron; 0.1 to 6 weight percent nickel; 0.1 to 6 weight percent manganese and balance substantially all copper. The iron stabilizes the alloy and reduces the rate of reactions when passing through critical temperatures and the like. The entire composition range of this alloy does not have a single phase structure, and thus provide more difficult working characteristics. Also, since alloying elements are often lost or volatized during welding processes, the preferred compositions of this patent utilizes the higher end of the disclosed alloying additions to compensate for such loss.
Therefore, none of the prior art discloses copper-nickel-aluminum alloy compositions that exhibit high ductility, reasonably high tensile strength, a broad range of fabricating options, a single phase structure, excellent corrosion resistance and the desired gold-like color, while capable of being made at low cost from scrap of rework materials.